Chapter 15 - Origin of Life

• Speciation has lead to the wide variety of life on earth seen today

• These processes have been ongoing since life first appeared on planet Earth

– Estimated formation of Earth occurred 4.6 billion years ago

– 1st fossil evidence of life is from about 3.5 billion years ago

• Stromatolite rocks contain evidence of photosynthetic bacteria

•Photosynthesis is a complex process, therefore life likely first arose between 3.6 and 4 billion years ago

• Fossil evidence suggests that these early organisms dominated the first 3/4 of the history of life on earth

• Early life has changed little since Prokaryotes first appeared on the plant

• All higher organisms have depended on these simple, single celled organisms

• By ~3 billion years ago, photosynthetic prokaryotes were producing enough oxygen to begin changing the atmosphere

Origin of Life

4 stage hypothesis:

– abiotic synthesis of ____________ and ______________

– joining of these molecules to form _____________ and _____________

– origin of self-replication

– packaging these materials within a membrane bound system (plasma membrane)

Could this actually happen?

• Miller-Urey experiment in 1954 showed that at least ___________ could be formed from material thought to be present in the atmosphere prior to the appearance of life

– ____

– ____

– ____

– ____

• Ancient meteorite also contained large number of amino acids, some similar to those recovered in the Miller-Urey experiment

Formation of larger polymers and membranes

• Wave action along ancient seas

• Heat from volcanic activity

• Combined these actions create a frothy mix

– Remember phospholipid bilay of the biological membranes forms spontaneously

– If these membranes trap organic compounds, they produce entities called protobionts

– Enzymatic proteins trapped in a protobiont carry out simple metabolic reactions

Self Replication

• RNA can also self-replicate under certain conditions

• Replication of complete cells – more complex but still feasible, especially when considered from a natural selection standpoint

Timeline of Evolution of Major Lineages of Life

• Prokaryotes evolved prior to _____ billion years ago

• Eukaryotic organisms first appeared _____ billion years ago

• Multicellular organisms _____ billion years ago

• True animals diversified about _____ million years ago

• Followed by land plants ______ million years ago

Evolution of Eukaryotes (Chapter 16)

· Serial Endosymbiosis

o Symbiotic relationship between a variety of prokaryotes

§ Mitochondria from ingested (but not digested) aerobic bacteria

§ Utilize excess ATP produced by the captive bacteria

§ Chloroplasts from ingested photosynthetic bacteria

§ Utilize sugars produces by these bacteria to generate ATP

§ Nucleus and Endoplasmic reticulum

§ Infolding of plasma membrane